整流变压器纵差保护二次侧电流最佳补偿方程及整定特征

Optimal Compensation Equation of Secondary Current and Setting Characteristics of Longitudinal Differential Protection for Rectifier Transformers

为弥补当前国内外大容量整流变压器只有过流保护而无纵差保护的缺失,论述了建立整流变压器纵差保护的关键内容。首先,提出并论证了整流变压器纵差保护阀侧电流互感器二次侧电流采样值的特殊处理方法,以及网阀两侧进入纵差保护CPU参与差动电流、制动电流计算的三相电流有效值应当采用何值,即论证其最佳补偿(或称转角)方程,它与常规电力变压器、换流变压器、电炉变压器等的补偿方程都不相同。然后,提出并论证了整流变压器阀侧两相短路时网侧电流相位及模值的独特计算方法。分析了两相短路及单相接地短路时整流变压器纵差保护的动作特性。整流变压器纵差保护整定计算特征能使整流变压器区内短路时动作灵敏度显著提高,并且使纵差保护的动作范围显著扩大,能保护整流桥的阀短路及直流输出端的短路故障。

To compensate for the current inadequacy of large capacity rectifier transformers with only overcurrent protection but no longitudinal differential protection at home and abroad, the key contents of setting up longitudinal differential protection for rectifier transformer are proposed. First, the special treatment methods for the sampled secondary current values of current transformer on the valve side of the longitudinal differential protection are put forward and demonstrated. And it is also shown what value of effective three-phase current values on the grid and valve sides in the calculation of differential current and brake current for longitudinal differential protection should be adopted, i.e., the best compensation （or angle） equation is demonstrated, which is different from the compensation equation of the conventional power transformer, converter transformer, electric furnace transformer, etc. A unique calculating method of phase and modulus value of grid-side current is proposed and demonstrated when a two phase short circuit fault occurs on the valve side of the rectifier transformer. The action characteristics of differential protection for rectifier transformer are analyzed when a two-phase short circuit fault or a single- phase grounding fault occurs. The characteristics of setting calculation of differential protection can make the protection action sensitivity significantly increase during the internal short-circuit fault, and make the differential protection range significantly expand, while protecting the valve-side short-circuit of the rectifier bridge and the DC side short-circuit.